The present application relates to a semiconductor structure and a method of forming the same. More particularly, the present application relates to a horizontal metal-insulator-metal (MIM) capacitor that is located within a same level as that of a back-end-of-the-line (BEOL) structure, and a method of forming such a MIM capacitor.
Capacitors are used extensively in electronic devices for storing an electric charge. Capacitors essentially comprise two conductive plates separated by an insulator. Capacitors can be used, for example, in filters, analog-to-digital converters, memory devices, various control applications, and mixed signal and analog devices.
There is a demand in semiconductor device technology to integrate many different functions on a single chip, e.g., manufacturing analog and digital circuitry on the same die. Metal-insulator-metal (MIM) capacitors are often used in these integrated circuits. A MIM capacitor is a particular type of capacitor which typically includes two metal plates sandwiched around a capacitor dielectric that is parallel to a surface of a semiconductor substrate. MIM capacitors are generally large in size, being several hundred micrometers wide, for example, depending on the capacitance, which is much larger than a transistor or memory cell, for example. MIM capacitors are typically used as decoupling capacitors for microprocessor units (MPU's), RF capacitors in high frequency circuits, and filter and analog capacitors in mixed-signal products.
To form a conventional MIM capacitor, the top capacitor metal plate is formed by a planar deposition of a conductive material. Next, the deposited conductive material is patterned by lithography and etching providing the top capacitor metal plate. The patterning of the top metal plate requires the use of a mask, and there can be alignment problems to underlying features (e.g., the MIM capacitor bottom plate) and vias to connect to interconnect layers.
Another problem in fabricating MIM capacitors is a restriction in the selection of the MIM dielectric materials, due to potential interaction with or diffusion of the metals (such as copper) used for the metal plates. The MIM dielectric material restriction may result in limited area capacitance.
A yet further problem in forming MIM capacitors is that, in order to avoid problems that arise in fabricating semiconductor devices using copper, often higher resistive plate materials such as, for example, aluminum, titanium nitride, and tungsten, are used for the top and bottom metal plates, which results in reduced high frequency capability. The use of copper, which has a lower resistivity, for the top and bottom metal plates is therefore desired. The use of copper for the top and bottom metal capacitor plates also produces a MIM capacitor having higher quality factors (Q-values).